1. Field of the Invention
The present invention relates generally to the detection of harmful plants. The present invention relates more particularly to methods for detecting urushiol-bearing plants such as poison ivy, poison oak, and poison sumac.
2. Technical Background
Urushiol is an oily mixture of catechol compounds having long chain alkyl or alkenyl substitution at their 3-positions. It occurs in the sap and resin of the leaves, vines and roots of a number of common plants, and can be released to the plant surface when fragile plant parts are cut or bruised. Urushiol can stay active for up to five years after release from the plant.
Many commonly-occurring plants bear urushiol. For example, poison ivy (Toxicondendron radicans) grows throughout the United States, primarily east of the Rockies. It can be a vine or shrub, and its most common leaf pattern is in groups of three with notched edges. Leaves are red in the spring, green in the summer, and can be a variety of colors with white berries in the fall. Poison oak (Toxicondendron diversilobum) grows predominantly west of the Rockies in the United States. It is typically a small bushy plant or climbing vine with leaves in groups of three, five or seven. It also changes leaf color throughout the season, with white berries present in the fall. Poison sumac (Toxicondendron vernix) is most common in the boggy areas of the south and northeast regions of the United States. It is a bush with seven to thirteen feather-like leaves per stem. It looks very similar to its non-toxic relative. The only way to distinguish the poisonous variety from the benign variety in the field is the color of the berries that appear during the fall; poison sumac has green berries, while sumac has red berries. There are a number of other urushiol bearing plants, each with a different appearance and range.
Urushiol can cause strong to severe allergic dermatitis, known as Rhus dermatitis, in humans. Direct skin-to-plant contact is the most frequent cause of exposure to urushiol, but it can also be indirectly transferred to skin via clothing, animal fur, garden tools and shoes. Rhus dermatitis typically begins with severe itching 8-48 hours after contact. The rash appears as red patches or small blisters progressing into red weeping blisters, and can last for three weeks if untreated. Urushiol contact can cause more severe reactions as well. For example, forestry workers and firefighters in the West can be exposed to smoke from burning poison oak, which can cause serious, sometimes lethal, lung irritation.
Allergic dermatitis caused by exposure to urushiol-bearing plants is not only very uncomfortable; it is nearly ubiquitous. With 85% of Americans likely to develop an allergic reaction to urushiol, it is the most common allergy in the country. Twenty-five to forty million Americans seek medical attention annually, and Rhus dermatitis accounts for 10% of the U.S.D.A. and U.S. Forestry Service's lost time.
While the itching of Rhus dermatitis can be ameliorated with any number of creams, antihistamine and steroidal treatments and home remedies, the better strategy is to avoid contact with urushiol-bearing plants altogether. Of course, while one can always wear long-sleeved shirts and long pants when in areas where urushiol-bearing plants may exist, this might make summertime activity rather uncomfortably warm. One can try to identify and avoid plants in the field (e.g., using identification cards). However, given their varying appearance and ability to camouflage themselves among other plants, urushiol-bearing plants can be extremely difficult to identify in the field. Accordingly, the average person will have great difficulty avoiding contact with the plants, and will be at risk of suffering the painful itching of Rhus dermatitis.
Accordingly, there remains a need for new methods to identify urushiol-bearing plants.